A witness told the Australian news programme Channel Nine TV: "There were no signs of obvious trauma. No blood or anything like that. No bones protruding.

"I saw the truck as well, hanging upside down, and couldn't believe he was still conscious."

An Ambulance Victoria spokeswoman said the driver remained in a critical condition, with serious head and pelvic injuries.

Images that surfaced just after the incident show the twisted wreckage of the heavy goods vehicle wrapped around the concrete barriers. The truck appears to have been flipped upside-down while the cargo dangles over the edge of the bridge.

Debris from the crash also hit a building below, cracking one of the brick walls. Subsequently, fire crews were called in to inspect the damage.

The other driver involved suffered minor injuries.

All inbound traffic on the busy Melbourne motorway was suspended as several cranes were brought in to secure the truck.

A remote-controlled drone was used to send live images back to the crane operator as the truck was pulled back from the brink.

The delicate operation took several hours to complete and train services, which run directly under the crash site, were also suspended.